In general, nitrogenous and phosphorus materials that result in eutrophication as well as organic materials are included in sewage.
If sewage including such nitrogenous and phosphorus materials flows in rivers, red tide or green tide occurs due to eutrophication that decreases dissolved oxygen in the river water, which may destroy the ecosystem and, further, contaminate a water supply system.
To solve such a problem, various advanced sewage treatment processes aimed at removing nitrogenous and phosphorus compounds as well as organic materials during the sewage treatment process have been proposed.
Among them, a sequencing batch reactor (SBR) process is a method for the treatment of sewage, in which a filling process, a reaction process, a settling process, a drawing process and an idle process proceed sequentially according to the lapse of time in a single reactor basin, that removes organics, nitrogenous and phosphorus compounds in sewage biologically using microorganisms in anaerobic, aerobic and anoxic conditions.
Dephosphorization reaction that discharges phosphorus from sewage occurs in the anaerobic condition of the SBR process. Organic decomposition, phosphorus absorption by microorganisms and nitrification reaction of sewage occur in the aerobic condition. Denitrification reaction of sewage takes place to remove nitrogen of sewage in the anoxic condition.
Since the SBR process uses a single reactor basin, the SBR process has advantages in that it is possible to reduce the size of sewage treatment facilities, it does not require a separate settling basin, and it provides convenience of operation with an automated facility, thus saving labor cost.
However, the SBR process using a single reactor basin has also some drawbacks in that time is required for converting the condition of the reactor basin into pure anaerobic, pure aerobic and pour anoxic conditions, respectively, since the anaerobic, aerobic and anoxic conditions are to be provided in the single reactor basin based on the lapse of time.
Accordingly, it is difficult to maintain the respective pure conditions separately in the SBR process using the single reactor basin. That is, if the anoxic process in which the nitrified sewage is denitrified is converted into the anaerobic condition, the denitrification reaction of the remaining nitrogen takes precedence, thus deteriorating dephosphorization efficiency and, further, phosphorus absorptance in the subsequent aerobic condition.